Electrolyte, lithium iron manganese phosphate battery and electric device

Abstract

The invention provides an electrolyte, a lithium iron manganese phosphate battery and an electric device. The electrolyte comprises a lithium salt and a solvent, the solvent comprises ethylene carbonate, propylene carbonate, ethyl methyl carbonate, fluorobenzene and a low-viscosity solvent in a volume ratio of (2-5): (2-5): (3-5): (3-5): (2-5). The high dielectric constants of ethylene carbonate and propylene carbonate improve the dissolving capacity of the electrolyte to lithium salt, and meanwhile, the molecular structure can form a stable interface layer on the surface of a positive electrode to inhibit migration and dissolution of manganese ions; due to the low viscosity characteristic of the low-viscosity solvent, the overall viscosity of the electrolyte is reduced, and the permeability of the porous positive electrode material is enhanced, so that the wettability is improved, and uniform de-intercalation of lithium ions is promoted; a physical adsorption protection layer can be formed on the surface of the positive electrode through the coordination effect of high-electronegativity fluorine atoms in fluorobenzene and manganese, and direct contact between manganese and electrolyte is further blocked.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to an electrolyte, and more particularly to an electrolyte, a lithium manganese iron phosphate battery, and an electric device. Background Technology

[0002] Lithium manganese iron phosphate (LMFP), like lithium iron phosphate, has an olivine structure and boasts advantages such as structural stability, high voltage platform, and high energy density, making it a novel high-energy cathode material. Due to the synergistic effect of Mn and Fe in LMFP, Fe and Mn can be miscible in any ratio to form a solid solution. Combining the stable electrochemical performance of lithium iron phosphate with the high voltage advantage of lithium manganese phosphate, LMFP exhibits higher energy density and higher safety than lithium iron phosphate.

[0003] In the existing technology, the electrolyte of lithium manganese iron phosphate batteries is usually the same as that of lithium iron phosphate batteries. When this type of electrolyte is used in conjunction with lithium manganese iron phosphate cathode material, it cannot improve manganese dissolution and has poor wettability with lithium manganese iron phosphate cathode material, which can easily lead to abnormal battery cycle degradation.

[0004] Existing technology discloses an electrolyte for lithium manganese iron phosphate batteries, its preparation method, and its application, belonging to the field of lithium-ion battery technology. The electrolyte disclosed in this document uses two components: component A contains conventional additives, and component B contains a novel positive electrode film-forming protective agent. These two components are injected using a specific method. Electrolyte component A is injected before formation, and through negative electrode formation reduction, a dense, low-resistance SEI film (negative electrode protective film) is formed, improving the cell's rate capability and cycle performance. Electrolyte component B is injected after cell formation, and through positive electrode oxidation during cycling, a CEI film (positive electrode protective film) is formed, preventing the dissolution of transition metal manganese and the oxidative decomposition of the electrolyte, further improving the cell's cycle performance. However, this electrolyte for lithium manganese iron phosphate batteries is difficult to sufficiently improve manganese dissolution and has poor wettability with the lithium manganese iron phosphate positive electrode material.

[0005] Existing technology discloses a suitable electrolyte for lithium manganese iron phosphate batteries and a lithium battery, relating to the field of lithium battery electrolytes, including lithium salts, organic solvents, and additives; wherein the lithium salts include: lithium difluorosulfonylimide and lithium hexafluorophosphate. The organic solvents include: ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate. The additives include: vinylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, lithium difluorophosphate, and tris(trimethylsilyl)phosphate. However, this suitable electrolyte for lithium manganese iron phosphate batteries also fails to adequately improve manganese dissolution and exhibits poor wettability with lithium manganese iron phosphate cathode materials.

[0006] Existing electrolytes all have certain drawbacks, including the inability to improve manganese dissolution and poor wettability with lithium manganese iron phosphate cathode materials, resulting in insufficient cycle performance of lithium manganese iron phosphate batteries. Therefore, it is crucial to develop and design a novel electrolyte, lithium manganese iron phosphate battery, and electric device. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an electrolyte, a lithium manganese iron phosphate battery, and an electric device. The electrolyte provided by the present invention comprises solvents including ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and a low-viscosity solvent. The high dielectric constants of ethylene carbonate and propylene carbonate enhance the electrolyte's ability to dissolve lithium salts, while their molecular structure forms a stable interface layer on the positive electrode surface, inhibiting manganese ion migration and dissolution. The low viscosity of the low-viscosity solvent reduces the overall viscosity of the electrolyte, enhancing its permeability to porous positive electrode materials, thereby improving wettability and promoting uniform lithium ion insertion / extraction, reducing manganese structure damage caused by localized stress. The coordination of the strongly electronegative fluorine atoms in fluorobenzene with manganese forms a physical adsorption protective layer on the positive electrode surface, further preventing direct contact between manganese and the electrolyte. These factors combined inhibit manganese dissolution from the lithium manganese iron phosphate positive electrode material and optimize its wettability.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides an electrolyte comprising a lithium salt and a solvent;

[0010] The solvent comprises ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and a low-viscosity solvent in a volume ratio of (2~5):(2~5):(3~5):(3~5):(2~5).

[0011] The volume ratio of ethylene carbonate to propylene carbonate in the solvent of this invention is (2~5):(2~5), for example, it can be 2:2, 2.5:2, 3:2, 3.5:2, 4:2, 4.5:2, 5:2, 2:2.5, 2.5:2.5, 3:2.5, 3.5:2.5, 4:2.5, 4.5:2.5, 5:2.5 or 5:5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] The volume ratio of ethylene carbonate to methyl ethyl carbonate in the solvent of this invention is (2~5):(3~5), for example, it can be 2:3, 2.5:3, 3:3, 3.5:3, 4:3, 4.5:3, 5:3, 2:3.5, 2.5:3.5, 3:3.5, 3.5:3.5, 4:3.5, 4.5:3.5, 5:3.5 or 5:5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] The volume ratio of ethylene carbonate to low-viscosity solvent in the solvent of this invention is (2~5):(3~5), for example, it can be 2:3, 2.5:3, 3:3, 3.5:3, 4:3, 4.5:3, 5:3, 2:3.5, 2.5:3.5, 3:3.5, 3.5:3.5, 4:3.5, 4.5:3.5, 5:3.5 or 5:5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] The volume ratio of ethylene carbonate to fluorobenzene in the solvent of this invention is (2~5):(2~5), for example, it can be 2:2, 2.5:2, 3:2, 3.5:2, 4:2, 4.5:2, 5:2, 2:2.5, 2.5:2.5, 3:2.5, 3.5:2.5, 4:2.5, 4.5:2.5, 5:2.5 or 5:5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] The low-viscosity solvent mentioned in this invention refers to an organic solvent with low viscosity in the electrolyte (such as dimethyl carbonate, ethyl methyl carbonate, or linear carboxylic acid esters).

[0016] The electrolyte provided by this invention comprises ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and a low-viscosity solvent. Ethylene carbonate (EC) and propylene carbonate (PC), as cyclic carbonates, possess high dielectric constants (EC has a dielectric constant of 89.6, and PC has a dielectric constant of 64.9), effectively dissolving lithium salts and forming stable ion pairs. Simultaneously, EC preferentially reduces on the negative electrode surface to form a dense SEI film, blocking side reactions between the electrolyte and the positive electrode material. Fluorobenzene exhibits strong electronegativity (fluorine atom electronegativity is 3.98), and its introduction can complex Mn. 2+The presence of ions inhibits the release of manganese ions from the crystal lattice through steric hindrance and electronic effects, forming [Mn-F] coordination bonds to suppress manganese dissolution. Ethyl methyl carbonate (EMC), as a chain carbonate (viscosity of 0.65 mPa·s at 25°C), significantly reduces the system viscosity. The ethoxy group (-OCH2CH3) in its molecule forms hydrogen bonds with the hydroxyl group (-OH) on the surface of lithium manganese iron phosphate, promoting the penetration of solvent molecules into the pores of the cathode material. The introduction of low-viscosity solvents reduces the overall viscosity of the electrolyte, further reducing interfacial tension, decreasing the solid-liquid interface contact angle, promoting electrolyte absorption, and improving lithium ion mobility and electrolyte permeability, thereby improving the electrochemical performance of the battery. These factors work together to inhibit the dissolution of manganese in the lithium manganese iron phosphate cathode material and optimize its wettability.

[0017] The electrolyte provided by this invention has a solvent in which the volume ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and low-viscosity solvent is (2~5):(2~5):(3~5):(3~5):(2~5), further reducing the dissolution of manganese in the lithium iron phosphate cathode material and improving the wettability of the lithium iron phosphate cathode material. Specifically, this volume ratio range ensures that the solvent contains sufficient cyclic carbonates (EC and PC) to provide a high dielectric constant for sufficient dissociation of the lithium salt; simultaneously, it contains sufficient EMC and a low-viscosity solvent, thereby reducing the overall viscosity to a low value and ensuring that the electrolyte has excellent ionic conductivity and electrode wettability. Furthermore, when the volume percentage of fluorobenzene is within this range, it can fully complex Mn. 2+ This allows it to inhibit dissolution; on the other hand, this volume ratio range avoids the negative effects of excess of any single component (such as increased viscosity or increased side reactions), thereby optimizing the performance of the electrolyte.

[0018] Preferably, the viscosity of the low-viscosity solvent is 0.55~0.78 mPa·s, for example, it can be 0.55 mPa·s, 0.58 mPa·s, 0.60 mPa·s, 0.62 mPa·s, 0.65 mPa·s, 0.68 mPa·s, 0.70 mPa·s, 0.72 mPa·s, 0.75 mPa·s or 0.78 mPa·s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] Preferably, the low-viscosity solvent includes any one or a combination of at least two of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Typical but non-limiting combinations include combinations of dimethyl carbonate and ethyl methyl carbonate, combinations of ethyl methyl carbonate and diethyl carbonate, combinations of dimethyl carbonate and diethyl carbonate, or combinations of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0020] The electrolyte provided by this invention includes a low-viscosity solvent, which can improve the poor wettability of thick electrodes, reduce the impedance of lithium manganese iron phosphate batteries, and improve the cycle performance of lithium manganese iron phosphate batteries.

[0021] The thick electrode mentioned in this invention refers to a positive or negative electrode structure in a lithium-ion battery that has a greater thickness (more than 100 μm) than traditional electrodes. Thick electrodes can increase the loading of active materials and store more energy in a limited volume, thereby significantly improving the energy density of the battery.

[0022] Preferably, the electrolyte further includes additives, including positive electrode film-forming additives, negative electrode film-forming additives, and positive and negative electrode film-forming additives.

[0023] Preferably, the positive electrode film-forming additive includes methylene methane disulfonate and / or propane sulfonyl lactone.

[0024] When the electrolyte provided by this invention includes methylene methane disulfonate and / or propane sulphol, methylene methane disulfonate and / or propane sulphol can form a stable CEI film on the surface of lithium manganese iron phosphate cathode particles, reducing the impact of Mn dissolution on the cell cycle performance and improving the cycle performance of lithium manganese iron phosphate batteries.

[0025] Preferably, the negative electrode film-forming additive includes any one or a combination of at least two of fluoroethylene carbonate, vinyl sulfate, or vinylene carbonate. Typical but non-limiting combinations include a combination of fluoroethylene carbonate and vinyl sulfate, a combination of vinyl sulfate and vinylene carbonate, a combination of fluoroethylene carbonate and vinylene carbonate, or a combination of fluoroethylene carbonate, vinyl sulfate, and vinylene carbonate.

[0026] When the electrolyte provided by the present invention includes any one or a combination of at least two of fluoroethylene carbonate, ethylene sulfate, or vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, or vinylene carbonate can reduce the internal resistance of lithium manganese iron phosphate batteries, thereby improving the electrochemical performance of lithium manganese iron phosphate batteries.

[0027] Preferably, the positive and negative electrode film-forming additives include any one or a combination of at least two of lithium difluorooxalate borate, lithium difluorophosphate, or lithium tetrafluoroborate. Typical but non-limiting combinations include combinations of lithium difluorooxalate borate and lithium difluorophosphate, combinations of lithium difluorophosphate and lithium tetrafluoroborate, combinations of lithium difluorooxalate borate and lithium tetrafluoroborate, or combinations of lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate.

[0028] When the electrolyte provided by this invention includes any one or a combination of at least two of lithium difluorooxalate borate, lithium difluorophosphate, or lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorophosphate, or lithium tetrafluoroborate can repair the CEI / SEI membrane damaged during cycling, thereby improving the cycle performance of lithium manganese iron phosphate batteries.

[0029] Preferably, the additive includes methylene disulfonate, propane sulpholactone, fluoroethylene carbonate, ethylene sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate.

[0030] Preferably, the mass ratio of methylene disulfonate, propane sulphol, fluoroethylene carbonate, vinyl sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate in the additive is (0.1~1):(0.1~1):(0.1~1):(0.1~1):(1~5):(0.1~4):(0.1~1):(0.1~1).

[0031] The mass ratio of methylene methane disulfonate to propane sulcolone in the additive of this invention is (0.1~1):(0.1~1), for example, it can be 0.1:0.1, 0.2:0.2, 0.3:0.3, 0.4:0.4, 0.5:0.5, 0.6:0.6, 0.7:0.7, 0.8:0.8, 0.9:0.9 or 1:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] The mass ratio of methylene methane disulfonate to fluoroethylene carbonate in the additive of this invention is (0.1~1):(0.1~1), for example, it can be 0.1:0.1, 0.2:0.2, 0.3:0.3, 0.4:0.4, 0.5:0.5, 0.6:0.6, 0.7:0.7, 0.8:0.8, 0.9:0.9 or 1:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] The mass ratio of methylene methane disulfonate to vinyl sulfate in the additive of this invention is (0.1~1):(0.1~1), for example, it can be 0.1:0.1, 0.2:0.2, 0.3:0.3, 0.4:0.4, 0.5:0.5, 0.6:0.6, 0.7:0.7, 0.8:0.8, 0.9:0.9 or 1:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] The mass ratio of methylene disulfonate to vinylene carbonate in the additive of this invention is (0.1~1):(1~5), for example, it can be 0.1:1, 0.2:1.5, 0.3:2, 0.4:2.5, 0.5:3, 0.6:3.5, 0.7:4, 0.8:4.5, 0.9:5 or 1:5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] The mass ratio of methylene methane disulfonate to lithium difluorooxalate borate in the additive of this invention is (0.1~1):(0.1~4), for example, it can be 0.1:0.1, 0.2:0.5, 0.3:1, 0.4:1.5, 0.5:2, 0.6:2.5, 0.7:3, 0.8:3.5, 0.9:4 or 1:4, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] The mass ratio of methylene methane disulfonate to lithium difluorophosphate in the additive of this invention is (0.1~1):(0.1~1), for example, it can be 0.1:0.1, 0.2:0.2, 0.3:0.3, 0.4:0.4, 0.5:0.5, 0.6:0.6, 0.7:0.7, 0.8:0.8, 0.9:0.9 or 1:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] The mass ratio of methylene methane disulfonate to lithium tetrafluoroborate in the additive of this invention is (0.1~1):(0.1~1), for example, it can be 0.1:0.1, 0.2:0.2, 0.3:0.3, 0.4:0.4, 0.5:0.5, 0.6:0.6, 0.7:0.7, 0.8:0.8, 0.9:0.9 or 1:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the mass ratio of the additive to the total mass of the lithium salt and solvent is (1.7~14):100, for example, it can be 1.7:100, 3:100, 4.5:100, 6:100, 7.5:100, 9:100, 10.5:100, 12:100, 13.5:100 or 14:100, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable; when the mass ratio of the additive to the total mass of the lithium salt and solvent in this invention is (1.7~14):100, the additive in the electric field... The interface film (SEI / CEI film) formed in the electrolyte reaches a dynamic equilibrium; the positive electrode film-forming additive forms a dense CEI film on the positive electrode surface, inhibiting manganese dissolution and electrolyte oxidative decomposition; the negative electrode film-forming additive forms a low-resistance SEI film on the graphite negative electrode, reducing lithium loss and the risk of lithium plating; at this ratio, it avoids both excessive additives leading to an overly thick interface film and increased impedance, and insufficient additives leading to incomplete interface passivation and side reactions, ultimately achieving synergistic optimization of ion transport efficiency, interface stability, and electrolyte compatibility, thereby improving the electrochemical performance of lithium manganese iron phosphate batteries.

[0039] Preferably, the lithium salt comprises lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide.

[0040] When the lithium salt in the electrolyte provided by this invention includes lithium bisfluorosulfonylimide, the stability of lithium manganese iron phosphate batteries can be enhanced because lithium bisfluorosulfonylimide has good stability.

[0041] Preferably, the concentration of lithium hexafluorophosphate in the electrolyte is 0.5~1 mol / L, and the concentration of lithium difluorosulfonylimide is 0.1~0.5 mol / L.

[0042] The concentration of lithium hexafluorophosphate in the electrolyte of the present invention is 0.5~1 mol / L, for example, it can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L or 1 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] The concentration of lithium difluorosulfonylimide in the electrolyte of the present invention is 0.1~0.5 mol / L, for example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L or 0.5 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] In a second aspect, the present invention provides a lithium manganese iron phosphate battery, wherein the lithium manganese iron phosphate battery includes the electrolyte described in the first aspect.

[0045] The lithium manganese iron phosphate battery provided in this invention includes a positive electrode, a negative electrode, a separator, and the electrolyte described in the first aspect. During the charging and discharging process of the lithium manganese iron phosphate battery, lithium ions repeatedly insert and extract between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, prevents short circuits between them while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts active ions.

[0046] The positive electrode of the lithium manganese iron phosphate battery provided by the present invention includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material. The positive electrode active material includes lithium manganese iron phosphate.

[0047] Preferably, in the lithium manganese iron phosphate battery provided by the present invention, the mass fraction of lithium manganese iron phosphate in the positive electrode film layer is 88%~93wt%, for example, it can be 88wt%, 88.5wt%, 89wt%, 89.5wt%, 90wt%, 90.5wt%, 91wt%, 91.5wt%, 92wt%, 92.5wt%, or 93wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. When the mass fraction of lithium manganese iron phosphate is 88%~93wt%, the energy density of the positive electrode film layer and the electrolyte permeation performance can be balanced, thereby making the lithium manganese iron phosphate battery exhibit better electrochemical performance.

[0048] Preferably, the positive electrode film layer may also optionally include a positive electrode conductive agent. There are no particular limitations on the type of positive electrode conductive agent in this invention. The positive electrode conductive agent can be any one or a combination of at least two of the following: superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typical but non-limiting combinations include combinations of superconducting carbon and conductive graphite, combinations of acetylene black and carbon black, combinations of Ketjen black and carbon dots, combinations of carbon nanotubes and graphene, combinations of graphene and carbon nanofibers, or combinations of superconducting carbon, conductive graphite, and acetylene black.

[0049] Preferably, the positive electrode film layer may optionally include a positive electrode binder; there is no particular limitation on the type of positive electrode binder in this invention, and the positive electrode binder may be at least one of polyvinylidene fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Typical but non-limiting combinations include combinations of polyvinylidene fluoride and polytetrafluoroethylene, combinations of ethylene-tetrafluoroethylene-propylene terpolymer and ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, combinations of tetrafluoroethylene-hexafluoropropylene copolymer and fluorinated acrylate resins, combinations of polyvinylidene fluoride, polytetrafluoroethylene and ethylene-tetrafluoroethylene-propylene terpolymer, or combinations of ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0050] Preferably, the positive electrode current collector can be a metal foil or a composite current collector. The metal foil includes aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. The metal material in the metal material layer may include any one or a combination of at least two of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material base layer may include any one or a combination of at least two of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0051] Preferably, the positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0052] Preferably, the negative electrode active material can be a negative electrode active material known in the art for use in secondary batteries. The negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy materials.

[0053] Preferably, the negative electrode film layer may also optionally include a negative electrode conductive agent. There are no particular limitations on the type of negative electrode conductive agent in this invention; the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0054] Preferably, the negative electrode film layer may also optionally include a negative electrode binder. There are no particular limitations on the type of negative electrode binder in this invention; the negative electrode binder may include at least one of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin (e.g., polyacrylic acid, polymethacrylic acid, or sodium polyacrylate), polyacrylamide, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0055] Preferably, the negative electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. The metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material base layer may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0056] Preferably, the negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone or deionized water, but is not limited to these.

[0057] Preferably, the negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, the negative electrode sheet also includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. Preferably, the negative electrode sheet in this invention also includes a protective layer covering the surface of the negative electrode film layer.

[0058] In the lithium manganese iron phosphate battery provided by the present invention, there are no particular restrictions on the type of separator used in the electrode assembly; any known porous separator with good chemical and mechanical stability can be selected.

[0059] Preferably, the material of the separator may include at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0060] Preferably, the positive electrode, the separator, the negative electrode, and the electrolyte can be used to make a lithium manganese iron phosphate battery.

[0061] Preferably, the outer packaging of the lithium manganese iron phosphate battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the individual battery cells can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic, such as at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0062] Thirdly, the present invention provides an electric device comprising the electrolyte described in the second aspect.

[0063] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] (1) The electrolyte provided by the present invention includes ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene and a low-viscosity solvent. Among them, ethylene carbonate (EC) and propylene carbonate (PC) are cyclic carbonates. Their high dielectric constants (EC has a dielectric constant of 89.6 and PC has a dielectric constant of 64.9) can effectively dissolve lithium salts and form stable ion pairs. At the same time, EC is preferentially reduced on the negative electrode surface to form a dense SEI film, blocking the side reactions between the electrolyte and the positive electrode material. Fluorobenzene has strong electronegativity (fluorine atom electronegativity is 3.98). The introduction of fluorobenzene can complex Mn. 2+ The presence of ions inhibits the release of manganese ions from the crystal lattice through steric hindrance and electronic effects, forming [Mn-F] coordination bonds to suppress manganese dissolution. Ethyl methyl carbonate (EMC), as a chain carbonate (viscosity of 0.65 mPa·s at 25°C), significantly reduces the system viscosity. The ethoxy group (-OCH2CH3) in its molecule forms hydrogen bonds with the hydroxyl group (-OH) on the surface of lithium manganese iron phosphate, promoting the penetration of solvent molecules into the pores of the cathode material. The introduction of low-viscosity solvents reduces the overall viscosity of the electrolyte, further reducing interfacial tension, decreasing the solid-liquid interface contact angle, promoting electrolyte absorption, and improving lithium ion mobility and electrolyte permeability, thereby improving the electrochemical performance of the battery. These factors work together to inhibit the dissolution of manganese in the lithium manganese iron phosphate cathode material and optimize its wettability.

[0066] (2) In the electrolyte provided by the present invention, the volume ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene and low-viscosity solvent is (2~5):(2~5):(3~5):(3~5):(2~5), which further reduces the dissolution of manganese in lithium iron phosphate cathode material and improves the wettability of lithium iron phosphate cathode material. On the one hand, this volume ratio range ensures that there are sufficient cyclic carbonates (EC and PC) in the solvent to provide a high dielectric constant for sufficient dissociation of lithium salt; at the same time, there is sufficient EMC and low-viscosity solvent, thereby reducing the overall viscosity to a low value and ensuring that the electrolyte has excellent ionic conductivity and electrode wettability; in addition, when the volume ratio of fluorobenzene is within this range, it can fully complex Mn. 2+ This allows it to inhibit dissolution; on the other hand, this volume ratio range avoids the negative effects of excess of any single component (such as increased viscosity or increased side reactions), thereby optimizing the performance of the electrolyte.

[0067] (3) When the electrolyte provided by the present invention includes methylene disulfonate and / or propane sulphol, methylene disulfonate and / or propane sulphol can form a stable CEI film on the surface of lithium manganese iron phosphate cathode particles, reduce the impact of Mn dissolution on the cycle performance of the cell, and improve the cycle performance of lithium manganese iron phosphate battery.

[0068] (4) When the electrolyte provided by the present invention includes any one or at least two of fluoroethylene carbonate, ethylene sulfate or vinylene carbonate, fluoroethylene carbonate, ethylene sulfate or vinylene carbonate can reduce the internal resistance of lithium manganese iron phosphate battery, thereby improving the electrochemical performance of lithium manganese iron phosphate battery.

[0069] (5) When the electrolyte provided by the present invention includes any one or at least two of lithium difluorooxalate borate, lithium difluorophosphate or lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorophosphate or lithium tetrafluoroborate can repair the CEI / SEI membrane damaged during the cycle, thereby improving the cycle performance of lithium manganese iron phosphate battery. Detailed Implementation

[0070] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0071] Example 1

[0072] This embodiment provides an electrolyte comprising lithium hexafluorophosphate at a concentration of 0.75 mol / L, lithium difluorosulfonylimide at a concentration of 0.3 mol / L, and a solvent;

[0073] The solvent comprises ethylene carbonate, propylene carbonate, ethyl methyl carbonate, fluorobenzene, and dimethyl carbonate in a volume ratio of 3.5:3.5:4:4:3.5.

[0074] The electrolyte also includes additives, the mass ratio of which to the total mass of lithium salt and solvent is 7.85:100.

[0075] The additives include methylene methane disulfonate, propane sulcolone, fluoroethylene carbonate, vinyl sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate in a mass ratio of 0.55:0.55:0.55:0.55:3:2.05:0.55:0.55.

[0076] Example 2

[0077] This embodiment provides an electrolyte comprising lithium hexafluorophosphate at a concentration of 0.5 mol / L, lithium difluorosulfonylimide at a concentration of 0.5 mol / L, and a solvent;

[0078] The solvent comprises ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and dimethyl carbonate in a volume ratio of 2:5:3:5:2.

[0079] The electrolyte also includes additives, wherein the mass ratio of the additives to the total mass of the lithium salt and solvent is 14:100.

[0080] The additives include methylene disulfonate, propane sulphol, fluoroethylene carbonate, ethylene sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate in a mass ratio of 0.1:1:0.1:1:1:4:0.1:1.

[0081] Example 3

[0082] This embodiment provides an electrolyte comprising lithium hexafluorophosphate at a concentration of 0.5 mol / L, lithium difluorosulfonylimide at a concentration of 0.1 mol / L, and a solvent;

[0083] The solvent comprises ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and dimethyl carbonate in a volume ratio of 2:2:3:3:2.

[0084] The electrolyte also includes additives, wherein the mass ratio of the additives to the total mass of the lithium salt and solvent is 1.7:100.

[0085] The additives include methylene disulfonate, propane sulcolone, fluoroethylene carbonate, ethylene sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate in a mass ratio of 0.1:0.1:0.1:0.1:0.1:0.1:0.1:0.1.

[0086] Example 4

[0087] This embodiment provides an electrolyte comprising lithium hexafluorophosphate at a concentration of 1 mol / L, lithium difluorosulfonylimide at a concentration of 0.5 mol / L, and a solvent;

[0088] The solvent comprises ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and dimethyl carbonate in a volume ratio of 5:5:5:5:5.

[0089] The electrolyte also includes additives, wherein the mass ratio of the additives to the total mass of the lithium salt and solvent is 14:100.

[0090] The additives include methylene disulfonate, propane sulphol, fluoroethylene carbonate, ethylene sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate in a mass ratio of 1:1:1:1:5:4:1:1.

[0091] Example 5

[0092] This embodiment provides an electrolyte comprising lithium hexafluorophosphate at a concentration of 0.8 mol / L, lithium difluorosulfonylimide at a concentration of 0.2 mol / L, and a solvent;

[0093] The solvent comprises ethylene carbonate, propylene carbonate, ethyl methyl carbonate, fluorobenzene, and dimethyl carbonate in a volume ratio of 4:3:5:3:4.

[0094] The electrolyte also includes additives, the mass ratio of which to the total mass of lithium salt and solvent is 5:100.

[0095] The additives include methylene disulfonate, propane sulcolone, fluoroethylene carbonate, ethylene sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate in a mass ratio of 0.8:0.3:0.7:0.2:2:3:0.9:0.4.

[0096] Example 6

[0097] This embodiment provides an electrolyte that is identical to that in Example 1, except that the methylene disulfonate and propane sulpholactone in the additives are omitted.

[0098] Example 7

[0099] This embodiment provides an electrolyte that is identical to that in Example 1, except that the additives fluoroethylene carbonate, ethylene sulfate, and vinylene carbonate are omitted.

[0100] Example 8

[0101] This embodiment provides an electrolyte that is identical to that in Example 1, except that lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate are omitted from the additives.

[0102] Example 9

[0103] This embodiment provides an electrolyte that is identical to that in Example 1, except that the ratio of the mass of the additive to the total mass of the lithium salt and solvent is 1:100.

[0104] Comparative Example 1

[0105] This comparative example provides an electrolyte that is identical to that of Example 1, except that ethylene carbonate in the solvent is omitted.

[0106] Comparative Example 2

[0107] This comparative example provides an electrolyte that is identical to that of Example 1, except that fluorobenzene in the solvent is omitted.

[0108] Comparative Example 3

[0109] This comparative example provides an electrolyte that is identical to that in Example 1, except that the volume ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene and dimethyl carbonate in the solvent is 2:5:3:8:2.

[0110] Comparative Example 4

[0111] This comparative example provides an electrolyte that is identical to that of Example 1, except that dimethyl carbonate in the solvent is omitted.

[0112] Application Example 1

[0113] This application example provides a lithium manganese iron phosphate battery, the manufacturing process of which is as follows:

[0114] A slurry was prepared by mixing olivine-type lithium manganese iron phosphate active material (90% by mass), conductive carbon black (7% by mass), PVDF binder (3% by mass) with NMP solvent, coated onto aluminum foil, vacuum dried at 120°C for 12 hours, compacted, and cut to obtain a positive electrode sheet. A slurry was prepared by mixing graphite (96% by mass), conductive agent (2% by mass), carboxymethyl cellulose (2% by mass) with water, coated onto copper foil, dried at 100°C, and rolled to obtain a negative electrode sheet. The obtained positive electrode sheet / polyethylene separator / positive electrode sheet were stacked and packaged into a CR2032 coin cell. After vacuum injection of the electrolyte provided in Example 1 above, the cell was allowed to stand for 24 hours. It was then pre-charged to 3.8V with a small current of 0.05C and aged at 50°C for 48 hours.

[0115] Application Example 2

[0116] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in Example 2 is vacuum injected.

[0117] Application Example 3

[0118] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in Example 3 is vacuum injected.

[0119] Application Example 4

[0120] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in Example 4 is vacuum injected.

[0121] Application Example 5

[0122] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in example 5 is vacuum injected.

[0123] Application Example 6

[0124] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in Example 6 is vacuum injected.

[0125] Application Example 7

[0126] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in Example 7 is vacuum injected.

[0127] Application Example 8

[0128] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in Example 8 is vacuum injected.

[0129] Application Example 9

[0130] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in Example 9 is vacuum injected.

[0131] Application Example 10

[0132] This application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the olivine-type lithium manganese iron phosphate active material (98% by mass), conductive carbon black (1.5% by mass), PVDF binder (0.5% by mass) are mixed with NMP solvent to form a slurry.

[0133] Comparative Application Example 1

[0134] This comparative application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in comparative example 1 is vacuum injected.

[0135] Comparative Application Example 2

[0136] This comparative application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in comparative example 2 is vacuum injected.

[0137] Comparative Application Example 3

[0138] This comparative application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in comparative example 3 is vacuum injected.

[0139] Comparative Application Example 4

[0140] This comparative application example provides a lithium manganese iron phosphate battery, which is the same as application example 1 except that the electrolyte provided in comparative example 4 is vacuum injected.

[0141] The CR2032 coin cells obtained from the above application examples and comparative application examples were kept at 25℃ and 45℃ for 2 hours respectively, and then charged and discharged 100 times at 0.2C (charging: 0.2C to 4.2V, constant voltage to 0.05C; discharging: 0.2C to 2.5V). The number of cycles when the capacity of the CR2032 coin cells at 25℃ and 45℃ was 80% is shown in Table 1.

[0142] At 25°C, the obtained CR2032 button cell was charged at a constant current of 0.5C to a voltage of 4.2V, and then charged at a constant voltage of 4.2V to a current of 0.05C. The DC resistance (DCR) of the battery was measured and is shown in Table 1.

[0143] Table 1

[0144]

[0145] From Table 1, we can obtain:

[0146] (1) The lithium manganese iron phosphate batteries prepared using the electrolytes provided in Application Examples 1 to 5 of the present invention have low DC resistance and exhibit good cycle performance at both low and high temperatures.

[0147] (2) By comparing Application Example 1 and Application Example 6, it can be seen that when the electrolyte provided by the present invention includes methylene methane disulfonate and / or propane sulphol, methylene methane disulfonate and / or propane sulphol can form a stable CEI film on the surface of lithium manganese iron phosphate cathode particles, reduce the impact of Mn dissolution on the cycle performance of the cell, and improve the cycle performance of lithium manganese iron phosphate battery.

[0148] (3) By comparing Application Example 1 and Application Example 7, it can be seen that when the electrolyte provided by the present invention includes any one or at least two of fluoroethylene carbonate, ethylene sulfate or vinylene carbonate, fluoroethylene carbonate, ethylene sulfate or vinylene carbonate can reduce the internal resistance of lithium manganese iron phosphate battery, thereby improving the electrochemical performance of lithium manganese iron phosphate battery.

[0149] (4) By comparing Application Example 1 and Application Example 8, it can be seen that when the electrolyte provided by the present invention includes any one or at least two of lithium difluorooxalate borate, lithium difluorophosphate or lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorophosphate or lithium tetrafluoroborate can repair the CEI / SEI membrane damaged during the cycle, thereby improving the cycle performance of lithium manganese iron phosphate battery.

[0150] (5) By comparing Application Example 1 and Application Example 9, it can be seen that the ratio of the mass of the additive in the electrolyte provided by the present invention to the total mass of lithium salt and solvent affects the performance of the lithium manganese iron phosphate battery; when the ratio of the mass of the additive to the total mass of lithium salt and solvent is (1.7~14):100, the lithium manganese iron phosphate battery prepared with this electrolyte has better performance. This is because when the ratio of the mass of the additive to the total mass of lithium salt and solvent is (1.7~14):100, the interface film (SEI) formed by the additive in the electrolyte is better. The positive electrode film-forming additive forms a dense CEI film on the positive electrode surface, inhibiting manganese dissolution and electrolyte oxidation decomposition; the negative electrode film-forming additive forms a low-resistance SEI film on the graphite negative electrode, reducing lithium loss and lithium plating risk; at this ratio, it avoids both excessive additives leading to an overly thick interfacial film and increased impedance, and insufficient additives leading to incomplete interfacial passivation and side reactions, ultimately achieving synergistic optimization of ion transport efficiency, interfacial stability and electrolyte compatibility, thereby improving the electrochemical performance of lithium manganese iron phosphate batteries;

[0151] (6) By comparing Application Example 1 and Application Example 10, it can be seen that in the lithium manganese iron phosphate battery provided by the present invention, taking the mass of the positive electrode film layer as 100%, the mass fraction of lithium manganese iron phosphate in the positive electrode film layer will affect the performance of the lithium manganese iron phosphate battery. When the mass fraction of lithium manganese iron phosphate in the positive electrode film layer is 88%~93wt%, the lithium manganese iron phosphate battery has better electrochemical performance. This is because when the mass fraction of lithium manganese iron phosphate is 88%~93wt%, it can balance the energy density of the positive electrode film layer and the electrolyte permeability. While ensuring that the lithium manganese iron phosphate battery has a high energy density, it makes the electrolyte and the positive electrode film layer more compatible, that is, the electrolyte has better permeability to the positive electrode film layer, so that the lithium manganese iron phosphate battery exhibits better electrochemical performance.

[0152] (7) By comparing Application Example 1 with Comparative Application Examples 1 to 4, it can be seen that the solvent of the electrolyte provided by the present invention includes ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene and a low-viscosity solvent. Among them, ethylene carbonate (EC) and propylene carbonate (PC), as cyclic carbonates, have high dielectric constants (EC has a dielectric constant of 89.6 and PC has a dielectric constant of 64.9), which can effectively dissolve lithium salts and form stable ion pairs. At the same time, EC is preferentially reduced on the negative electrode surface to form a dense SEI film, blocking the side reactions between the electrolyte and the positive electrode material. Fluorobenzene has strong electronegativity (fluorine atom electronegativity is 3.98), and the introduction of fluorobenzene can complex Mn. 2+ The presence of ions inhibits the release of manganese ions from the crystal lattice through steric hindrance and electronic effects, forming [Mn-F] coordination bonds to suppress manganese dissolution. Ethyl methyl carbonate (EMC), as a chain carbonate (viscosity of 0.65 mPa·s at 25°C), significantly reduces the system viscosity. The ethoxy group (-OCH2CH3) in its molecule forms hydrogen bonds with the hydroxyl group (-OH) on the surface of lithium manganese iron phosphate, promoting the penetration of solvent molecules into the pores of the cathode material. The introduction of low-viscosity solvents reduces the overall viscosity of the electrolyte, further reducing interfacial tension, decreasing the solid-liquid interface contact angle, promoting electrolyte absorption, and improving lithium ion mobility and electrolyte permeability, thereby improving the electrochemical performance of the battery. These factors work together to inhibit the dissolution of manganese in the lithium manganese iron phosphate cathode material and optimize its wettability.

[0153] The electrolyte provided by this invention has a solvent in which the volume ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and low-viscosity solvent is (2~5):(2~5):(3~5):(3~5):(2~5), further reducing the dissolution of manganese in the lithium iron phosphate cathode material and improving the wettability of the lithium iron phosphate cathode material. Specifically, this volume ratio range ensures that the solvent contains sufficient cyclic carbonates (EC and PC) to provide a high dielectric constant for sufficient dissociation of the lithium salt; simultaneously, it contains sufficient EMC and a low-viscosity solvent, thereby reducing the overall viscosity to a low value and ensuring that the electrolyte has excellent ionic conductivity and electrode wettability. Furthermore, when the volume percentage of fluorobenzene is within this range, it can fully complex Mn. 2+ This allows it to inhibit dissolution; on the other hand, this volume ratio range avoids the negative effects of excess of any single component (such as increased viscosity or increased side reactions), thereby optimizing the performance of the electrolyte.

[0154] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises lithium salt and solvent; The solvent comprises ethylene carbonate, propylene carbonate, methyl ethyl carbonate, fluorobenzene, and a low-viscosity solvent in a volume ratio of (2~5):(2~5):(3~5):(3~5):(2~5).

2. The electrolyte according to claim 1, characterized in that, The viscosity of the low-viscosity solvent is 0.55~0.78 mPa·s; Preferably, the low-viscosity solvent includes any one or a combination of at least two of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate.

3. The electrolyte according to claim 1 or 2, characterized in that, The electrolyte also includes additives, including positive electrode film-forming additives, negative electrode film-forming additives, and positive and negative electrode film-forming additives.

4. The electrolyte according to claim 3, characterized in that, The positive electrode film-forming additive includes methylene methane disulfonate and / or propane sulcolone. Preferably, the negative electrode film-forming additive includes any one or a combination of at least two of fluoroethylene carbonate, ethylene sulfate, or vinylene carbonate; Preferably, the positive and negative electrode film-forming additives include any one or a combination of at least two of lithium difluorooxalate borate, lithium difluorophosphate, or lithium tetrafluoroborate.

5. The electrolyte according to claim 3 or 4, characterized in that, The additives include methylene disulfonate, propane sulphol, fluoroethylene carbonate, vinyl sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate.

6. The electrolyte according to claim 5, characterized in that, The mass ratio of methylene disulfonate, propane sulcolone, fluoroethylene carbonate, vinyl sulfate, vinylene carbonate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium tetrafluoroborate in the additive is (0.1~1):(0.1~1):(0.1~1):(0.1~1):(1~5):(0.1~4):(0.1~1):(0.1~1).

7. The electrolyte according to any one of claims 3 to 6, characterized in that, The mass ratio of the additive to the total mass of the lithium salt and solvent is (1.7~14):

100.

8. The electrolyte according to any one of claims 1 to 7, characterized in that, The lithium salt includes lithium hexafluorophosphate and / or lithium difluorosulfonylimide; Preferably, the concentration of lithium hexafluorophosphate in the electrolyte is 0.5~1 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide is 0.1~0.5 mol / L.

9. A lithium manganese iron phosphate battery, characterized in that, The lithium manganese iron phosphate battery includes the electrolyte as described in any one of claims 1 to 8.

10. An electric device, characterized in that, The electric device includes the electrolyte as described in claim 9.

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